U.S. patent application number 16/624598 was filed with the patent office on 2020-04-23 for contactless voltage transducer.
The applicant listed for this patent is LEM International SA. Invention is credited to Felix Buhlmann, Dominik Schlafli, Wolfram Teppan.
Application Number | 20200124643 16/624598 |
Document ID | / |
Family ID | 59350689 |
Filed Date | 2020-04-23 |
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United States Patent
Application |
20200124643 |
Kind Code |
A1 |
Buhlmann; Felix ; et
al. |
April 23, 2020 |
CONTACTLESS VOLTAGE TRANSDUCER
Abstract
Contactless voltage transducer for measuring voltages between at
least two conductors of an alternating voltage conductor system,
the transducer including two or more capacitive current measurement
units, each said capacitive current measurement unit comprising an
electrode surrounding a passage for receiving therethrough a
respective said conductor of the alternating voltage conductor
system, an electrode shield surrounding the electrode, an electrode
signal processing circuit portion connected to the electrode and
electrode shield, configured to output an analog measurement
signal, and a reference voltage signal generator connected to the
electrode shield and configured to generate a reference voltage
source signal, wherein the reference voltage signal generators of
the two or more capacitive current measurement units are connected
together at a common floating voltage connection point.
Inventors: |
Buhlmann; Felix; (Lausanne,
CH) ; Schlafli; Dominik; (Nyon, CH) ; Teppan;
Wolfram; (Wunnewil, CH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LEM International SA |
Plan-les-Ouates |
|
CH |
|
|
Family ID: |
59350689 |
Appl. No.: |
16/624598 |
Filed: |
July 10, 2018 |
PCT Filed: |
July 10, 2018 |
PCT NO: |
PCT/EP2018/068620 |
371 Date: |
December 19, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01R 19/2513 20130101;
G05F 3/08 20130101; G01R 15/142 20130101; H03M 1/001 20130101; G01R
15/16 20130101 |
International
Class: |
G01R 15/16 20060101
G01R015/16; G01R 19/25 20060101 G01R019/25; G01R 15/14 20060101
G01R015/14; G05F 3/08 20060101 G05F003/08; H03M 1/00 20060101
H03M001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 12, 2017 |
EP |
17181076.5 |
Claims
1.-16. (canceled)
17. Contactless voltage transducer for measuring voltages between
at least two conductors of an alternating voltage conductor system,
the transducer including two or more capacitive current measurement
units, each said capacitive current measurement unit comprising: an
electrode surrounding a passage for receiving therethrough a
respective said conductor of the alternating voltage conductor
system, an electrode shield surrounding the electrode, an electrode
signal processing circuit portion connected to the electrode and
electrode shield, configured to output an analog measurement
signal, and a reference voltage signal generator connected to the
electrode shield and configured to generate a reference voltage
source signal, wherein the reference voltage signal generators of
the two or more capacitive current measurement units are connected
together at a common floating voltage connection point.
18. The contactless voltage transducer according to claim 17,
wherein the conductor system is a multiphase conductor system and
the transducer comprises one capacitive current measurement unit
for each phase of the electrical conduction system and in addition
one for a neutral conductor.
19. The contactless voltage transducer according to claim 18,
wherein the conductor system is a two phase or three phase
conductor system.
20. The contactless voltage transducer according to claim 17,
further comprising an external electrostatic shield surrounding
said two or more capacitive current measurement units, and an
additional reference voltage signal generator connected to the
external electrostatic shield and the common floating voltage
connection point.
21. The contactless voltage transducer according to claim 17,
wherein the reference voltage signal generators are configured to
generate said reference voltage source signals at frequencies
higher than the alternating voltage frequency of the conductor
system.
22. The contactless voltage transducer according to claim 17,
wherein at least two of the reference voltage signal generators are
configured to generate said reference voltage source signal at
different frequencies from each other.
23. The contactless voltage transducer according to claim 22,
wherein each of the reference voltage signal generators are
configured to generate said reference voltage source signal at a
frequency different from the others.
24. The contactless voltage transducer according to claim 17,
comprising a microcontroller circuit configured to compute an
electrode-conductor admittance matrix Y from the reference voltage
source signals and associated currents output by the capacitive
current measurement units.
25. The contactless voltage transducer according to claim 24,
wherein the microcontroller circuit comprises a digital-to-analog
converter (DAC) for generating the reference Voltage signals and an
analog-to-digital converter (ADC) for receiving and processing the
analog measurement signal response from the output capacitive
currents from each electrode.
26. The contactless voltage transducer according to claim 25,
wherein the transducer comprises an energy harvesting unit
configured to harvest power from the conductors of the system to be
measured, the energy harvesting unit comprising one or more
induction coils arranged axially adjacent, or coaxially around one
or more of the electrodes, for mounting around one or more of the
conductors.
27. The contactless voltage transducer according to claim 17,
wherein the transducer comprises an autonomous power source in the
form of a battery.
28. The contactless voltage transducer according to claim 17,
wherein the transducer comprises a wireless communications module
connected to the processor of the transducer to transmit wirelessly
the measurement signals, and to receive commands or requests from
an external system.
29. A fully autonomous contactless voltage transducer without any
direct electrical connections to external systems, for measuring
voltages between at least two conductors of an alternating voltage
conductor system or an external system, the transducer including a
wireless communications module to transmit wirelessly measurement
signals, and two or more capacitive current measurement units, each
said capacitive current measurement unit comprising: an electrode
surrounding a passage for receiving therethrough a respective said
conductor of the alternating voltage conductor system, an electrode
shield surrounding the electrode, an electrode signal processing
circuit portion connected to the electrode and electrode shield,
configured to output an analog measurement signal, and a reference
voltage signal generator connected to the electrode shield and
configured to generate a reference voltage source signal, wherein
the reference voltage signal generators of the two or more
capacitive current measurement units are connected together at a
common floating voltage connection point.
30. The autonomous contactless voltage transducer according to
claim 29, wherein the conductor system is a multiphase conductor
system and the transducer comprises one capacitive current
measurement unit for each phase of the electrical conduction system
and in addition one for a neutral conductor.
31. Method of measuring voltages between at least two conductors of
an alternating voltage conductor system without a galvanic
connection, comprising: providing a contactless voltage transducer
according to claim 17, generating reference voltage signals
V.sub.i.sup.ref and measuring corresponding output capacitive
current signals I.sub.i.sup.ref of the electrodes, identifying in a
processing circuit of the transducer an admittance Y matrix based
on the reference voltage signals and corresponding output
capacitive current signals, computing, in the processing circuit of
the transducer, an impedance matrix Z obtained from the admittance
matrix Y, providing an identification of the conductor system.
32. Method according to claim 31, comprising: measuring electrode
currents I.sub.i.sup.meas of the conductor system, and computing in
a processing circuit of the transducer, using the impedance matrix
Z, the alternating voltage to be measured between said at least two
conductors.
33. The autonomous contactless voltage transducer according to
claim 30, wherein the conductor system is a two phase or three
phase conductor system.
34. The autonomous contactless voltage transducer according to
claim 29, further comprising an external electrostatic shield
surrounding said two or more capacitive current measurement units,
and an additional reference voltage signal generator connected to
the external electrostatic shield and the common floating voltage
connection point.
35. The autonomous contactless voltage transducer according to
claim 29, wherein the reference voltage signal generators are
configured to generate said reference voltage source signals at
frequencies higher than the alternating voltage frequency of the
conductor system.
36. The autonomous contactless voltage transducer according to
claim 29, wherein at least two of the reference voltage signal
generators are configured to generate said reference voltage source
signal at different frequencies from each other.
37. The autonomous contactless voltage transducer according to
claim 36, wherein each of the reference voltage signal generators
are configured to generate said reference voltage source signal at
a frequency different from the others.
38. The autonomous contactless voltage transducer according to
claim 29, comprising a microcontroller circuit configured to
compute an electrode-conductor admittance matrix Y from the
reference voltage source signals and associated currents output by
the capacitive current measurement units.
39. The autonomous contactless voltage transducer according to
claim 38, wherein the microcontroller circuit comprises a
digital-to-analog converter (DAC) for generating the reference
Voltage signals and an analog-to-digital converter (ADC) for
receiving and processing the analog measurement signal response
from the output capacitive currents from each electrode.
40. The autonomous contactless voltage transducer according to
claim 39, wherein the transducer comprises an energy harvesting
unit configured to harvest power from the conductors of the system
to be measured, the energy harvesting unit comprising one or more
induction coils arranged axially adjacent, or coaxially around one
or more of the electrodes, for mounting one or more of the
conductors.
41. The autonomous contactless voltage transducer according to
claim 29, wherein the transducer comprises an autonomous power
source in the form of a battery.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a transducer for measuring
alternating voltages in in a contactless manner.
BACKGROUND OF THE INVENTION
[0002] It is known to measure alternating (AC) voltages and
relative phases between two to or more conductors (typically three
phases and neutral) without interrupting and contacting the
conductors. The conductors may for instance be in the form of
electrical cables, and for instance a capacitive transducer with a
split electrode is placed around each of the cables. The
contactless transducer facilitates installation and decreases
hazards to personnel and equipment, especially in hazardous voltage
applications.
[0003] In order to reduce the effect of the unknown coupling
capacitances between the cables and the transducer, and thus to
enhance measurement precision, two (or more) reference voltage
sources may be used as described in U.S. Pat. No. 5,473,244.
[0004] A main drawback of the system described in U.S. Pat. No.
5,473,244, and also in other contactless voltage measurement
systems such as described in U.S. Pat. No. 6,470,283, is the need
to have a ground terminal. Access to a ground connection at the
position of installation of the voltage measurement transducer may
not be readily available, and the need to install a galvanic
connection increases the cost and complexity of the voltage
measurement setup.
[0005] Moreover, for hazardous voltage applications, the need to
implement a galvanic connection may increase risks to safety of
personnel installing, maintaining or using the measurement
equipment.
SUMMARY OF THE INVENTION
[0006] In view of the foregoing, it is an object of this invention
to provide a contactless voltage transducer that is accurate and
reliable, without requiring a ground connection.
[0007] It would be advantageous to provide a contactless voltage
transducer that is safe and easy to install.
[0008] It would be advantageous to provide a contactless voltage
transducer that is cost effective to manufacture and install.
[0009] Objects of this invention have been achieved by providing
the contactless voltage transducer according to claim 1 or claim
13, and a method according to claim 15.
[0010] Disclosed herein is a contactless voltage transducer for
measuring voltages between at least two conductors of an
alternating voltage conductor system, the transducer including two
or more capacitive current measurement units, each said capacitive
current measurement unit comprising [0011] an electrode surrounding
a passage for receiving therethrough a respective said conductor of
the alternating voltage conductor system, [0012] an electrode
shield surrounding the electrode, [0013] an electrode signal
processing circuit portion connected to the electrode and electrode
shield, configured to output an analog measurement signal, and
[0014] a reference voltage signal generator connected to the
electrode shield and configured to generate a reference voltage
source signal, [0015] wherein the reference voltage signal
generators of the two or more capacitive current measurement units
are connected together at a common floating voltage connection
point.
[0016] Also disclosed herein is a fully autonomous contactless
voltage transducer without any direct electrical connections to
external systems, for measuring voltages between at least two
conductors of an alternating voltage conductor system of an
external system, the transducer including a wireless communications
module to transmit wirelessly measurement signals, and two or more
capacitive current measurement units, each said capacitive current
measurement unit comprising [0017] an electrode surrounding a
passage for receiving therethrough a respective said conductor of
the alternating voltage conductor system, [0018] an electrode
shield surrounding the electrode, [0019] an electrode signal
processing circuit portion connected to the electrode and electrode
shield, configured to output an analog measurement signal, and
[0020] a reference voltage signal generator connected to the
electrode shield and configured to generate a reference voltage
source signal, [0021] wherein the reference voltage signal
generators of the two or more capacitive current measurement units
are connected together at a common floating voltage connection
point.
[0022] In an advantageous embodiment, the conductor system is a
multiphase conductor system and the transducer comprises one
capacitive current measurement unit for each phase of the
electrical conduction system and in addition one for a neutral
conductor.
[0023] In an advantageous embodiment, the transducer may further
comprise an external electrostatic shield surrounding said two or
more capacitive current measurement units, and an additional
reference voltage signal generator connected to the external
electrostatic shield and the common floating voltage connection
point.
[0024] In an advantageous embodiment, the reference voltage signal
generators are configured to generate said reference voltage source
signals at frequencies higher than the alternating voltage
frequency of the conductor system.
[0025] In an advantageous embodiment, at least two of the reference
voltage signal generators are configured to generate said reference
voltage source signal at different frequencies from each other.
[0026] In an embodiment, each of the reference voltage signal
generators may be configured to generate said reference voltage
source signal at a frequency different from the others.
[0027] In an embodiment, the voltage transducer may comprise a
microcontroller circuit configured to compute an
electrode-conductor admittance matrix Y from the reference voltage
source signals and associated currents output by the capacitive
current measurement units.
[0028] In an embodiment, the microcontroller circuit comprising a
digital-to-analog converter (DAC) for generating reference Voltage
signals and an analog-to-digital converter (ADC) for receiving and
processing the analog measurement signal response from the output
capacitive currents from each electrode.
[0029] Also disclosed herein is a method of measuring voltages
between at least two conductors of an alternating voltage conductor
system without a galvanic connection, comprising: [0030] providing
a contactless voltage transducer as described above, [0031]
generating reference voltage signals V.sub.i.sup.ref and measuring
corresponding output capacitive current signals I.sub.i.sup.ref of
the electrodes, [0032] identifying in a processing circuit of the
transducer an admittance matrix Y based on the reference voltage
signals and corresponding output capacitive current signals, [0033]
computing, in the processing circuit of the transducer, an
impedance matrix Z obtained from the admittance matrix Y, providing
an identification of the conductor system.
[0034] The method may further comprise [0035] measuring electrode
currents I.sub.i.sup.meas of the conductor system, and [0036]
computing in a processing circuit of the transducer, using the
impedance matrix Z, the alternating voltage to be measured between
said at least two conductors.
[0037] Further objects and advantageous aspects of the invention
will be apparent from the claims, and from the following detailed
description and accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] The invention will now be described with reference to the
accompanying drawings, which by way of example illustrate the
present invention and in which:
[0039] FIG. 1 is a schematic simplified diagram of an electrical
layout of a contactless voltage transducer according to an
embodiment of the invention;
[0040] FIG. 2 is a schematic simplified diagram of the contactless
voltage transducer of FIG. 1 for one of the phases, illustrating
capacitive couplings between conductive elements of the
transducer;
[0041] FIG. 3 is a schematic simplified diagram of an equivalent
circuit representing the contactless voltage transducer.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0042] Referring to the figures, a contactless voltage transducer 2
according to an embodiment of the invention comprises two or more
capacitive current measurement units 3, each comprising an
electrode surrounding a passage 6 for receiving therethrough a
respective conductor 1, 1n of a conductor system comprising at
least two conductors, at least one of which carries an alternating
voltage.
[0043] In an embodiment, the conductors of the conductor system may
belong to a multi-phase alternating voltage electrical conduction
system. The electrical conduction system may be two-phase, three
phase or have four or more phases, and may comprise in additional a
neutral conductor. It may however be noted that the invention is
not limited to a multiphase system and may be applied to any
conductors that exhibit a relative alternating voltage between
measured conductors.
[0044] The conductors may for instance be in the form of
conventional insulated wires or cables, or insulated conductor rods
or bars, or have other per se known configurations. In a variant,
the conductors may also be uninsulated, the contactless voltage
transducer comprising an insulating layer on the electrodes
configured to dielectrically separate the electrode from the
uninsulated conductor.
[0045] The electrodes 4 may completely surround the conductor
passage 6, or may only partially surround the conductor passage 6,
for instance leaving a gap to allow insertion of the conductor in
the passage 6.
[0046] The electrode may be provided in a housing with a movable
portion to allow insertion of the conductor to be measured in a
corresponding passage 6 of an electrode.
[0047] The contactless voltage transducer 2 is configured for
measuring relative alternating voltages between any two or more
conductors 1, 1n of the conduction system. The contactless voltage
transducer 2 may also be configured for measuring relative phases
between any two or more conductors 1, 1n of the conduction
system.
[0048] Each capacitive current measurement unit 3 further comprises
an electrode shield 8 surrounding the electrode 4, an electrode
signal processing circuit connected to the electrode 4 and
electrode shield 8, configured to output an analog measurement
signal S.sub.1, S.sub.2, S.sub.3, S.sub.4, and a voltage signal
generator 10 connected to the measurement shield and configured to
generate a voltage signal V.sub.1, V.sub.2, V.sub.3, V.sub.4. The
voltage signal generators 10 of the plurality of capacitive current
measurement units are connected together at a common floating
voltage connection point 11.
[0049] The contactless voltage transducer 2 may further comprise an
analog-digital processing circuit 12 configured for processing the
analog measurement signals S.sub.1 . . . S.sub.4.
[0050] In an embodiment, the voltage transducer may further
comprise an external shield 14 surrounding a plurality of the
capacitive current measurement units 3.
[0051] In an embodiment, the analog-digital processing circuit 12
includes a microcontroller circuit comprising a digital-to-analog
converter (DAC) for generating reference voltage signals and an
analog-to-digital converter (ADC) for receiving and processing the
analog measurement signal S.sub.1, S.sub.2, S.sub.3, S.sub.4
response.
[0052] The invention relies on the principle of measuring
capacitive currents between electrodes and the conductors over
initially unknown capacitances. To measure those capacitances,
additional (small) known voltage signals are applied on the
electrode shield by the voltages generators, such that voltages and
currents can be determined, and in turn the impedances can be
calculated.
[0053] The electrodes are on a potential relatively close to each
other, thus enabling a single electronic system to process the
measurements from all conductors of the multi-conductor conduction
system. The electrostatic shield around all the electrodes and the
electrodes simplifies the system of coupling impedances.
[0054] In prior art systems, in order to determine and thus adjust
for the capacitive currents that pass via unknown earth
capacitances, the transducer is calibrated using a voltage source
connected to an earth potential, injecting a known voltage of high
frequency between two electrodes. In the present invention however,
a ground connection is not needed, whereby the voltage sources are
connected to a floating point voltage. The transducer according to
embodiments of the present invention may be provided without any
connection to external conductors. The transducer according to
embodiments of the present invention may thus may be installed
without any electrical connections to the conductors to be measured
or the device or equipment in which the transducer may be
installed. Advantages include increased ease of installation and
increased safety.
[0055] Referring to the figures, in the illustrated embodiments,
each conductor 1 is capacitively coupled (capacitance C.sub.1) to
an electrode 4 and the electrode is surrounded by a shield 8
capacitively coupled to the electrode 4 (capacitance C.sub.2) and
the conductor 1 (capacitance C.sub.3). An associated capacitive
current through the electrode may be measured by the signal
processing circuit portion 16 when a voltage is applied to the
shield 8 by the voltage generator 10. The signal processing circuit
portion may for instance be a current-to-voltage conversion
circuit, which in its simplest form may consist in a resistor
across which a voltage output corresponding to the capacitive
current, is measured. In the illustrated embodiment, the signal
processing circuit comprises an operational amplifier which accepts
as input the capacitive current and gives an output voltage that is
proportional to the capacitive input current. The illustrated
exemplary circuit arrangement is also known as a transresistance
amplifier.
[0056] Each voltage generator 10 supplies a reference alternating
voltage source to the electrode shield (for example a sinusoidal
waveform with a frequency of 1 kHz) which generates an output
signal S.sub.1 . . . S.sub.4 corresponding to the currents I.sub.1
. . . I.sub.4 driven by those voltage sources V.sub.1 . . .
V.sub.4. The reference alternating voltage source V.sub.1 . . .
V.sub.4 and measured output currents I.sub.1 . . . I.sub.4 may be
used to obtain the previously unknown electrode-conductor
admittances matrix Y.
[0057] In an embodiment, an extra voltage source V.sub.S may also
be used to drive the outermost electrostatic shield 14 of the
transducer. In a variant, the system may comprise a plurality of
assembled shielded enclosures with electrodes connected to a
central shielded unit through shielded cables, each shielded
enclosure enclosing one or a plurality of the capacitive current
measurement units 3.
[0058] The admittance matrix Y is processed in a microcontroller of
the transducer to obtain the impedance matrix Z. With the impedance
matrix Z, the unknown voltages on the conductors 1, 1n can be
determined from a measurement of the currents flowing from the
conductors 1, 1n to the electrodes 4 at a known or identified
alternating voltage frequency f. The known or identified frequency
f may for instance be a mains frequency of 50 Hz or 60 Hz with an
essentially sinusoidal characteristic. The invention however may be
implemented in conductor systems with other alternating voltage
frequencies, or conductor systems carrying multitone voltage
signals, or conductor systems with alternating voltages exhibiting
non-sinusoidal characteristics.
[0059] In the invention it is also possible to estimate the quality
of the system identification using the voltage reference signals,
and if this quality degrades, to automatically and adaptively
change the processing method, for instance by changing the voltage
reference signals, by changing the filtering time constant or other
process parameters in order to offer the optimal response for
identifying the system under various conditions. For instance, when
the system changes quickly, long time constants are not conducive
to a better estimate, and in such case it is better to switch to a
filter time constant that is in line with the system time
constants. The errors may be higher than for a stable system, but
smaller than when applying non-optimal filtering.
[0060] Signal processing for a contactless voltage transducer with
a two conductor system (example neutral and phase or phase to
phase) comprising a driven outermost shield will now be described
by way of example. The exemplified processing for a two conductor
system can easily be adapted to a system with more conductors,
whereby the admittance matrix is augmented with a corresponding
number of columns and lines.
[0061] The signal processing according to the invention comprises
two important processing steps carried out by a processing circuit
of the transducer: [0062] admittance Y matrix identification from
the measurement using the reference/calibrating voltage sources
V.sub.i.sup.ref, [0063] conductor voltages computation using the
impedance Z matrix obtained from the Admittance Y matrix
identification and the measured electrode currents
I.sub.i.sup.meas.
[0064] Y Matrix Identification
[0065] The admittance matrix Y gives a relation between voltages
and currents in the system (see FIG. 3).
( I 1 ref I 2 ref ) = ( Y 11 Y 12 Y 15 Y 21 Y 22 Y 25 ) ( V 1 ref V
2 ref V 5 ref ) with ##EQU00001## Y ij = I ij ref V j ref , with V
k ref .perp. V j ref and V k ' meas .perp. V j ref ##EQU00001.2##
for k .noteq. j , all k ' ##EQU00001.3##
[0066] I.sub.ij.sup.ref is the current in branch j generated by the
reference source of branch j. V.sub.j.sup.ref is the reference
source of branch j. I.sub.ij.sup.ref and V.sub.j.sup.ref are
complex numbers.
[0067] The relationship between the injected reference voltages
V.sup.ref, the measured resulting capacitive currents I.sup.ref,
and the admittance matrix may be expressed in a generalized compact
form as:
I.sup.refY(j.omega.)V.sup.ref
[0068] Y.sub.ij is in the general case a complex number or even a
complex function of frequency Y(.omega.). In the present example,
we identify the admittance matrix Y only at one frequency and we
correct, translate or scale it (see Y*.sub.ij below) for other
frequencies. If the electrode-conductor system is only capacitive,
then the real part of the admittance matrix Y is zero (i.e. there
are assumed to be no resistive losses). This is however not the
case if the dielectric surrounding the conductor (PVC or other) has
losses. Here V.sub.k.sup.ref .perp. V.sub.j.sup.ref means that the
source labeled k can be distinguished from V.sub.j.sup.ref source,
for example if the sources are switched on one after one, or each
source is a sinusoidal signal with a different frequency, or
various other characteristics. For instance one may have the
voltage reference generators producing orthogonal signals (with 0
cross correlation). These signals could be a form of bandwidth
limited pseudorandom sequence, covering the bandwidth of the signal
to be measured, but long enough that the probability distribution
for the cross correlation with the signal to be measured stays
close to a very low value for most of the time. The important point
is to use reference voltage waveforms so that the current
I.sub.ij.sup.ref in branch i generated by the source
V.sub.j.sup.ref in branch j can be determined without any
ambiguity. The same is valid for the reference voltage waveforms
and the measured voltage waveforms (such as 50 Hz or 60 Hz
conduction systems and their possible harmonics).
[0069] In an embodiment, one may for instance use sinus waveforms
for reference voltage sources with different frequencies just above
100 Hz (i.e. 127 Hz, 113 Hz, and 109 Hz). In that manner, the
reference voltage sources can be distinguished easily from each
other and from the voltage waveforms that are measured (such as 50
Hz or 60 Hz power systems and their possible harmonics). However,
in variants, other methods can be used to identify and characterize
the system.
[0070] In an embodiment, the reference voltage signals may be
generated in a plurality of different frequencies on each line by
the corresponding voltage generator, for instance at 40 Hz, 60 Hz,
80 Hz, 100 Hz and 120 Hz in order to generate a plurality of
admittance matrices to better identify and characterize the system,
taking into account the effects that varying voltages may have on
the identified impedances of the system. In an embodiment, the
reference voltage signals may be in the form of a multitone signal,
or a signal that comprises non-sinusoidal wave forms.
[0071] More generally, the reference voltage signals may generate
any sequence of signals that are at least partially orthogonal to
the signal to measure and at least partially orthogonal to the
other reference signals. The response to this reference voltage
signal sequence may be extracted through correlation.
[0072] In an embodiment, the admittance matrix Y may be calculated
in the following approximated manner (even though the real and the
imaginary parts do not necessarily have the same frequency
dependence). We can approximate that the real part, which can be
associated to dielectric losses, should be small. The imaginary
part, associated to the capacitive conductor-electrode coupling, is
frequency dependent. This simplified approximated method gives good
results when dielectric losses are small (but should be adjusted if
dielectric losses are high).
Y ij * = I ij ref V j ref f meas f j ref ##EQU00002##
[0073] Conductor Voltage Computation with Impedance Matrix Z
[0074] The impedance matrix Z is computed from the admittance
matrix Y. In the general case, the impedance matrix Z is the
pseudoinverse of the admittance matrix Y.
Z=pinv(Y)
[0075] In the present example we use
Z*=pinv(Y*)F
[0076] With the impedance matrix Z, we can now compute the
conductor voltage V.sub.i.sup.meas from the current
I.sub.i.sup.meas generated by these sources in the electrodes.
( V 1 meas V 2 meas V 5 meas ) = ( Z 11 * Z 12 * Z 21 * Z 22 * Z 51
* Z 52 * ) ( I 1 meas I 2 meas ) ##EQU00003##
[0077] In a compact form this may be generalized as:
V.sup.meas=Z*I.sup.meas
[0078] The voltage difference between conductor i and j is given by
(also valid for the outer shield)
V.sub.ij.sup.meas=V.sub.i.sup.meas-V.sub.j.sup.meas
[0079] In the example discussed above, the admittance matrix
includes the reference voltage of the shield V.sub.5.sup.ref,
however the latter may be optional and in such case the calculation
of the admittance matrix Y would be simplified to:
( I 1 ref I 2 ref ) = ( Y 11 Y 12 Y 21 Y 22 ) ( V 1 ref V 2 ref )
##EQU00004##
[0080] In this case the system becomes square and we can compute
the voltage difference V.sub.21.sup.meas between conductor 1 and 2
based on the following relations:
Z * = inv ( Y * ) ##EQU00005## ( V 1 meas V 2 meas ) = ( Z 11 * Z
12 * Z 21 * Z 22 * ) ( I 1 meas I 2 meas ) V 21 meas = V 2 meas - V
1 meas ##EQU00005.2##
[0081] In an embodiment, the transducer may further include onboard
an autonomous power source, such as a battery. In a variant the
transducer may comprise an energy harvesting unit configured to
harvest power for operation of the transducer from the conductors
of the system to be measured. The energy harvesting unit may for
instance comprise one or more induction coils arrange axially
adjacent, or coaxially around one or more of the electrodes, for
mounting around one or more of the conductors.
[0082] In an embodiment, the transducer may further include a
wireless communications module connected to the processor of the
transducer to transmit wirelessly the measurement signals, and to
receive commands or requests from an external system.
[0083] A fully autonomous wireless transducer without any galvanic
connections may thus be provided for easy and versatile
installation.
LIST OF REFERENCES IN THE DRAWINGS
[0084] 2 voltage transducer [0085] 3 capacitive current measurement
unit [0086] 4 measurement electrode [0087] 16 electrode signal
processing circuit [0088] 18 operational amplifier 20 inputs
(-V.sub.in, +V.sub.in) 22 output [0089] 6 passage [0090] 8
electrostatic electrode shield [0091] 10 voltage signal generator
[0092] 16 electrode signal processing circuit [0093] 12
analog/digital processing circuit [0094] 14 external electrostatic
shield
[0095] V Voltage
[0096] I Current
* * * * *